High accuracy measurement system for focusing and leveling

Abstract

The present disclosure provides a high accuracy measurement system for focusing and leveling. The system determines an off-focus distance in the perpendicular direction within the exposure field and an inclination in the horizontal direction by measuring heights of four detection points on a substrate by using a four-channel detection method, thereby achieving focusing and leveling of the substrate. The detection of the substrate heights is implemented by a focusing method based on dual-channel light intensity modulation. Two superposed grating fringes are formed with phase difference of π/2. The shift can be resolved by the phase variation of corresponding fringes. According to the method, the off-focus distance can be derived. The present disclosure effectively eliminates the error due to the intensity changes caused by the fluctuations of the source or the reflectance of the substrate surface. The apparatus for focusing and leveling is easy to be implemented and has an accuracy of nanoscale.

We claim: 
     
       1. A high accuracy measurement apparatus for adjusting and leveling a focal plane, wherein the measurement apparatus for focusing and leveling comprises a four-channel focusing measurement device including a first focusing measurement device (L 1 ), a second focusing measurement device (L 2 ), a third focusing measurement device (L 3 ) and a fourth focusing measurement device (L 4 ), respectively;
 the first focusing measurement device consists of an illuminating unit formed of a light source ( 1 ) and a lens ( 2 ), a label grating ( 3 ), a first image-side telecentric optical device ( 4 ), formed of two lens at the entrance side before a substrate ( 5 ), and a polarizer ( 6 ), an Savart plate ( 7 ), a photoelastic modulation device formed of beam splitters ( 81 ,  82 ), a phase adjustment plate ( 91 ,  92 ), a detection grating ( 10 ), a first object-side telecentric optical device, a second object-side telecentric optical device, a first photoelectric detector and a second photoelectric detector at a reflecting side after the substrate ( 5 ), in turn along a measuring light path; 
 the label grating ( 3 ) is imaged on a substrate ( 5 ) through the first telecentric optical device ( 4 ) with an incident angle of 86°; 
 the image reflected by the substrate ( 5 ) is divided into two beams by the beam splitter ( 81 , 82 ) after passing through the Savart plate, in which a first beam and a second beam are respectively imaged on the detecting grating ( 10 ); 
 the phase adjustment plate ( 91 , 92 ) is configured to ensure that the phase difference between the two beams is equal to π/2 when the image of the label grating ( 3 ) reflected by the substrate ( 5 ) is imaged onto the detection grating ( 10 ); 
 the first photoelectric detector ( 141 ) and the second photoelectric detector ( 142 ) are configured to detect the first beam transmission energy and the second beam transmission energy after forming a superposed grating by the label grating ( 3 ) and the detection grating ( 10 ); 
 the position information of the first photoelectric detector ( 141 ) and the second photoelectric detector ( 142 ) are fixed, and when the substrate ( 5 ) moves upwards and downwards, the positions of the image of label grating ( 3 ) and the detection grating ( 10 ) are also shifted; at the same time, the intensities detected by the first photoelectric detector ( 141 ) and the second photoelectric detector ( 142 ) are also varied; 
 the position of the focal plane of the substrate ( 5 ) is accurately measured by calculating a ratio of the signals detected by the first photoelectric detector ( 141 ) and the second photoelectric detector ( 142 ) after being processed; and 
 the structures of the second, the third and the fourth focusing measurement devices are identical to that of the first focusing measurement device. 
 
     
     
       2. The high accuracy measurement apparatus for focusing and leveling according to  claim 1 , wherein each of the four-channel focusing measurement device has the same structure and principle, and the detection points of the four-channel focusing measurement device are placed within an exposure field of the substrate, and are distributed on an X axis and Y axis coordinate system which are built based on the center of the exposure filed of the substrate, wherein two detection points are symmetrically placed on the X axis, and two detection points are symmetrically placed on the Y axis. 
     
     
       3. The high accuracy measurement device for focusing and leveling according to  claim 1 , wherein the parameters of the label grating and the detection grating are identical to each other, and these two gratings are both placed at a certain angle, such that the image of the label grating is parallel imaged onto the detection grating, wherein the length of the detection grating is sufficient to ensure that the first beam and the second beam after being split are both perpendicularly incident onto the detection grating without intersection and interference. 
     
     
       4. The high accuracy measurement device for focusing and leveling according to  claim 1 , wherein the photoelastic modulation device comprises a first quarter wave plate, a photoelastic modulator, a second quarter wave plate and a polarizer. 
     
     
       5. The high accuracy measurement apparatus for focusing and leveling according to  claim 1 , wherein a group of the beam splitters divides the beam after passing through the Savart plate into two beams having the same intensity and in the same propagation direction. 
     
     
       6. The high accuracy measurement apparatus for focusing and leveling according to  claim 1 , wherein the phase adjustment plate is configured to ensure that the phase difference between the first beam and the second beam is π/2 when the label grating is imaged onto the detection grating. 
     
     
       7. The high accuracy measurement apparatus for focusing and leveling according to  claim 1 , wherein the first image-side telecentric optical device includes an imaging module, which is an image-side telecentric imaging module or a double telecentric imaging module;
 each of the first object-side telecentric optical device and the second object-side telecentric optical device include an imaging module, which is an object-side telecentric imaging module or a double telecentric imaging module; 
 the first image-side telecentric optical device is placed at a certain angle with respect to the first object-side telecentric optical device and the second object-side telecentric optical device, to ensure that the grating image which is imaged onto the substrate by the first image-side telecentric optical device is reflected by the substrate, and then is imaged again on the detection grating to form a Moire fringe, and finally is received by the first photoelectric detector and the second photoelectric detector after passing through the first object-side telecentric optical device and the second object-side telecentric optical device, respectively. 
 
     
     
       8. The high accuracy measurement apparatus for focusing and leveling according to  claim 1 , wherein the first photoelectric detector and the second photoelectric detector are required to detect the intensities of the first beam and the second beam simultaneously.